1. Field of the Invention
The present invention relates to an electrically charged beam drawing technique for use in manufacturing a semiconductor device, and particularly to a pattern drawing system using an electrically charged beam by introducing a proximity effect correcting technique, an electrically charged beam drawing method, a photomask manufacturing method, and a semiconductor device manufacturing method.
2. Description of the Related Art
When forming a photomask used for manufacturing a semiconductor device, for example, a resist film applied on a mask substrate is irradiated with electron beams or electrically charged beams, and a mask pattern is graphically drawn on the resist film. The electron beams incident to the resist film at the time of this drawing transmit through this resist film, and are reflected from the mask substrate. Thus, the incident electrons are scattered. By these scattered electrons, the resist film is exposed again. The exposure by the scattered electrons covers a resist film beyond the contour of a preset drawing range using the incident electron beams and has an effect such as dimensional change on a pattern formed at the periphery of a drawn pattern. This phenomenon is known as a “proximity effect”. In this case, with respect to the electron irradiation quantity at an arbitrary drawing position on the resist film, the irradiation quantity of the scattered electrons incident at the drawing of another peripheral patterns is added to the set irradiation quantity. Therefore, in response to a coating rate of another peripheral patterns formed in a range in which the proximity effect is attained, an effective irradiation quantity at the drawing position changes, and a dimensional change such as pattern enlargement occurs with a mask pattern to be formed.
A method for restricting the proximity effect includes an “irradiation quantity correcting method” for restricting a dimensional change by changing an irradiation quantity of electrically charged beams at the drawing position so as to compensate for the irradiation quantity of the scattered electrons among the adjacent patterns. Conventionally, there has been a problem that the irradiation quantity correcting method requires a long calculation time because the coating rate of the peripheral patterns is calculated, and then, the irradiation quantity at the drawing position is calculated. However, in recent years, with the improvement of computer's calculation processing capability, the correction of an irradiation quantity has been successfully carried out in almost real time. This irradiation quantity correcting method has been widely used as a proximity effect correcting method.
On the other hand, there is a dimensional change factor of a pattern that depends on a pattern coating rate of a region wider than a region in which the proximity effect is attained. For example, there is a “fogging effect” that the electron beams reflected from a mask substrate are reflected again on a structure of a drawing device such as an objective lens, and the resist film is exposed again. The fogging effect caused by the reflected electron beams cover a wider range than that in the proximity effect. For example, in the case where a resist film is coated on a glass substrate, the range encompassed by the proximity effect is about 10 μm while the range encompassed by the fogging effect is about 1 cm. Therefore, when the irradiation quantity correcting method is employed to restrict a dimensional change caused by the fogging effect, a region for calculating a pattern coating rate is very large as compared with a region of the proximity effect, thus requiring a tremendously large amount of calculation time even with the recent computer's calculation processing capability. Thus, in order to more simply restrict a dimensional change factor such as a fogging effect whose range is wider than that of the proximity effect, there has been proposed a method for partitioning the whole drawing region into partitions, and then, adjusting the irradiation quantity in a unit partition in response to a pattern coating rate of patterns included in the unit partition.
Further, there has been proposed a method for applying, at the same time, both of: a correcting method capable of restricting a dimensional change factor that depends on a pattern coating rate in a narrow range, such as proximity effect correction; and a correcting method capable of restricting a dimensional change factor that depends on a pattern coating rate of a wide range, such as the fogging effect correction (see, for example, Jpn. Pat. Appln. KOKAI Publication No. 2003-133209). However, there has been a problem that a correction error rather increases more significantly due to a synergetic effect of proximity effect correction and fogging effect correction.